Retinoic acid modulation of mrna levels in malignant, nontransformed, and immortalized osteoblasts

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Abstract
Clonal cell lines presumably “arrested” at a particular stage of differentiation are useful models to study the processes of differentiation in osteoblasts. UMR‐201 is a presumptive preosteoblastic nontransformed rat clonal cell line with a limited life span in culture. Two immortalized cell lines, UMR‐201‐10A (10A) and UMR‐201‐10B (10B), were derived from UMR‐201 by stable transfection with simian virus (SV) 40 large T antigen. This study compares the growth and profile of gene expression of the immortalized cell lines with those of UMR‐201 and UMR‐106‐06, a rat clonal cell line with well‐defined osteoblast‐like phenotypic characteristics. All four cell lines constitutively expressed the mRNA for the γ, α, and β receptors for retinoic acid (RA), the growth hormone receptor, pro‐α1(I) collagen, osteonectin, bone proteoglycan I, and bone morphogenetic proteins (BMP) 1 and 2A. Alkaline phosphatase mRNA was absent in the preosteoblast cell lines but was induced by treatment with 10−6 M RA, which also increased the steady‐state levels of mRNA for osteopontin and BMP1. mRNA for matrix gla protein was constitutively present and further induced by RA in UMR‐201 and 10B only. Messenger RNA for bone sialoprotein and bone morphogenetic protein 3 were constitutively expressed in UMR‐106‐06 and UMR‐201 but absent in the immortalized cell lines. None of the cell lines expressed measurable mRNA for bone gla protein or bone proteoglycan II. 10B grew more rapidly than UMR‐201, but unlike UMR‐201, it was also able to proliferate in serum‐free medium and exhibit anchorage‐independent growth. In summary, this study identifies novel retinoic acid effects on gene expression in these cells. Differences noted in the expression of mRNAs between UMR‐106‐06 and the other cell lines may provide some insight into the sequence of expression of these phenotypic characteristics as osteoblasts differentiate.
Funding Information
  • National Health and Medical Research Council

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